This is a program to study the Cell Biology of Striated Muscle. It was established in 1977 to support a program combining biochemical, physiological and ultrastructural approaches to the understanding of control of excitation and contraction in cardiac and skeletal muscle. Five project leaders develop general inter-related themes, including: - functional role and developmental pattern of myosin heavy chain isozymes, especially their response to circulatory and hormonal influences. - characterization of the genes coding for myosin heavy chains and for membrane channels, and determination of the factors controlling the gene expression. - kinetic properties of the actomyosin interaction, its regulation, and its relationship to cross-bridge events during contraction. - structural basis of conduction, including the cardiac gap junction and the sarcolemmal transport and Na-channel proteins, and their functional counter parts in cardiac cells under voltage clamp. - control of intracellular calcium and its relation to tension in muscle. These studies are organized into six projects and three core facilities. We have had significant progress in defining the structure-function relationships and the genetic control of several important components of the surface membrane and the contractile system.